1. Field of the Invention
This invention relates generally to communication systems, and, more particularly, to wireless communication systems.
2. Description of the Related Art
Conventional wireless communication systems include one or more base stations, which may also be referred to as node-Bs, for providing wireless connectivity to one or more mobile units, which may also be referred to using terms such as user equipment, subscriber equipment, and access terminals. Exemplary mobile units include cellular telephones, personal data assistants, smart phones, text messaging devices, laptop computers, desktop computers, and the like. Each base station may provide wireless connectivity via Radio Frequency (RF) signals to one or more mobile units in a geographical area, or cell, associated with the base station. For example, a base station that operates according to a Universal Mobile Telecommunication System (UMTS) protocol may provide wireless connectivity to one or more mobile units in a cell associated with the base station over a wireless communication link.
The wireless communications link typically includes one or more antennae mounted to a tower. In some applications, the antennae may be controllably tilted to change the Radio Frequency (RF) environment according to a predetermined plan or to accommodate dynamic changes in the RF environment. The antennae are typically equipped with actuators, such as RET actuators, which may be used to remotely control the positioning or tilt of a particular antenna.
Typically, the base station includes a bus system that carries electrical power for the actuators and other equipment (e.g., low-noise receive path amplifiers). Some devices within the base station need electrical power to provide their functionality, such as receive gain amplification or electrically driven RET actuators. Thus, it is useful if the power on the bus is not interrupted. Current interruption may occur if the current drawn by the devices within the base station exceeds the maximum available over the bus system. The current drawn by these devices can vary substantially, depending on the state of the device. For example, an idle RET actuator usually draws only a relatively small idle current, while an operating RET actuator can draw significantly more current. Other equipment draws current depending on their operational state, i.e. more current is drawn when the device has failed. In some prior art systems, operation of the devices may be scheduled to prevent excessive current draw. In particular, ordinarily only one RET actuator may be permitted to move at a time.
The disadvantage of this approach is that not all of the actuators that move the antennae of the same base station can be moved at the same time, and thus, negative effects to the RF environment are induced during the time any of the antennae is in the process of being positioned or tilted. This repositioning process can take up to several minutes, depending on the tilt angle change. Accordingly, periods of poor performance may be experienced while each of the antennae is repositioned.
Another disadvantage is that a single point of failure exists for the power management of the bus. If an overcurrent situation arises, a loss of power on the bus can cause the low noise receive amplifiers or electrically driven RET actuators to stop working. For RET actuators, the loss of power can result in lost calibration information, which in turn requires re-calibration of the RET actuator. Until re-calibration can be effected, the base station may interfere with neighboring cells or the affected cell may experience a loss of service.